1. Field of the Invention
The present invention relates to an apparatus and method for controlling a supply voltage, and more particularly to an apparatus and method for controlling a supply voltage of a multiple interface card for interfacing with a plurality of hosts.
2. Description of the Related Art
A smart card such as a SIM (Subscriber Identification Module) card is installed in a card holder/acceptor inside a mobile phone. Since the SIM card stores subscriber information including the subscriber's telephone directory, a subscriber can use a second mobile phone as if it is the subscriber's first mobile phone by transferring the SIM card into the second mobile phone.
However, SIM cards generally have a small storage capacity, which may be insufficient for certain applications such as a mobile phone requiring both an identification function and a multimedia storage function. Multiple interface cards are currently under development. Multiple interface cards can receive different supply voltages from a plurality of hosts, either simultaneously or sequentially. The different supply voltages are converted by a supply voltage control apparatus into operating voltages which can be used by CPUs or peripheral devices.
FIG. 1 is a block diagram of a supply voltage control apparatus 100 of a conventional multiple interface card. Referring to FIG. 1, the supply voltage control apparatus 100 includes a first supply voltage receiver 110 for receiving a first supply voltage from a first host (not shown) and a second supply voltage receiver 120 for receiving a second supply voltage from a second host (not shown). The first and second supply voltages are converted by a first voltage adjustment unit 130 and a second voltage adjustment unit 140, respectively, into voltages used by an internal circuit 150.
The first host and the second host operate independently. In general, the first host and the second host can use different supply voltages, and each host can either block or provide supply voltages independently of the other host.
However, in the conventional supply voltage control apparatus 100 shown in FIG. 1 an inverse voltage can be generated. An inverse voltage occurs when the second supply voltage is supplied to the first host or the first supply voltage is supplied to the second host. In the conventional supply voltage control apparatus 100, when either the first or second supply voltage is blocked or interrupted while both the first and second supply voltages are being supplied, the first or second host can be destroyed due to an inverse voltage.